Originally Posted by
scifi
I don't know what range they use when deciding to offer Traffic advice, but it seems to be about 3-5 miles, which with two planes on a closing heading, gives you about 60 seconds warning of the other aircraft.
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See CAP493 (downloadable) Section 1: Chapter 12: UK Flight Information Services - Page 6
Note 1: Traffic is normally considered to be relevant when, in the judgement of the controller, the conflicting aircraft’s observed trajectory indicates that it will pass within 3 NM and, where level information is available, 3,000 ft of the aircraft in receipt of the Traffic Service or its level-band if manoeuvring within a level block. However, controllers may also use their judgment to decide on occasions when such traffic is not relevant, e.g. passing behind or within the parameters but diverging. Controllers shall aim to pass information on relevant traffic before the conflicting aircraft is within 5 NM, in order to help the pilot meet his collision avoidance responsibilities and to allow time for an update in traffic information if considered necessary.
Note 2: Good judgement is essential to ensure that traffic information is relevant and timely. Controllers should take account of the aircraft's relative speeds, lateral and vertical closure rates, and track histories.
Note 3: Distances displayed on ATS surveillance systems can be at variance to the actual distances between aircraft due to limitations inherent to surveillance systems. Some aircraft may not be displayed at all.